Lipids, with various physiological functions, are a major group of materials present in biological systems, besides proteins, saccharides, and nucleic acids. Lipids also represent an important group of industrial products manufactured for nutritional, medical, cosmetic, hygienic, environmental, and numerous other applications. Some important examples of lipids for nutritional and medical uses include the monosaturated lipids for healthy diets, which offer the following potential benefits: decreased risk of breast cancer, heart disease and stroke; reduced cholesterol levels and belly fat; less pain and stiffness for those with rheumatoid arthritis; and weight loss; and the omega-3 fatty acids, e.g., docosahexaenoic acid (DHA), with reported health benefits to brain, eye and heart, and included in infant formula.
More recently, with the heightened awareness of global warming and depleting petroleum sources, there has been very strong demand for production of renewable fuel and chemicals. Large-scale industrial production of lipids using microorganisms plays an important role in meeting this demand. For renewable fuel the microbial lipids can be converted to biodiesel (methyl or ethyl esters of fatty acids), hydrocarbons, and jet fuel. The lipids can also serve as feedstock for the production of various chemicals. For industrial production processes, the productivity, product concentration and yield (i.e., percent conversion of substrate to product) are very important factors to be maximized for overall economics. One common limitation in microbial processes for production of intracellular lipids is the low intracellular lipid contents achievable.
Thus lipid content should be maximized for economic purposes, i.e., high productivity, high product concentrations, and high yield (i.e., % conversion of substrate to product). However, beyond certain concentrations, organic acids are inhibitory/toxic to cells themselves. This can limit lipid contents inside the cells. The present invention induces formation of insoluble lipid droplets/particles in algae so the lipid contents can be very high.